The major objective of the collaborative study is to determine the clinical efficacy and safety of L-Alpha-Acetylmethadol (LAAM). The elements of the study are: 1) Comparing the safety and efficacy of LAAM and Methadone on an open trial for 40 weeks on two groups of heroin addicts. 2) Continuation of study patients for an additional 40 weeks of LAAM treatment. 3) Electrocardiographic studies on LAAM and Methadone patients and comparisons with normal controls. 4) Admission of women of non-childbearing potential as study patients. All patients are identically managed with respect to medical, social and vocational services. Safety is evaluated by regular, systematic patient monitoring consisting of close medical support and recording of signs, symptoms and extensive laboratory surveillance. The major criteria for determining efficacy are the changes in social adjustment, arrest rate, employment, the use of illicit drugs and the rate of retention. The continuation study known as "Vanguard" would evaluate the safety profile of long-term LAAM maintenance for another 40 weeks. During this phase, women heroin addicts shall be included, and sub-study on cardiac status will be implemented. The significance of this study lies in the expected improved health care delivery for heroin addicts, as it implicates less involvement in drug seeking behavior and increased potential for rehabilitative measures. A decreased traffic in illicit Methadone would also prove beneficial to the community. Sixteen treatment facilities following a similar protocol will increase the generalizability of results. The study will be coordinated by staff of SAODAP, with the help of a scientific advisory board.